CdTe Particles Research Articles

Multifunctional light-controllable nanozyme enabled bimodal fluorometric/colorimetric sensing of mercury ions at ambient pH

Nanomaterials with enzyme-like catalytic features (nanozymes) find wide use in analytical sensing. Apart from catalytic characteristics, some other interesting functions coexist in the materials. How to combine these properties to design multifunctional nanozymes for new sensing strategy development is challenging. Besides, in nanozymes it is still a challenge to conveniently control the catalytic process, which also hinders their further applications in advanced biochemical analysis. To remove the above barriers, here we design a light-controllable multifunctional nanozyme, namely manganese-inserted cadmium telluride (Mn–CdTe) particles, that integrates oxidase-like activity with luminescence together, to achieve the fluorometric/colorimetric dual-mode detection of toxic mercury ions (Hg2+) at ambient pH. The Mn–CdTe exhibits a light-triggered oxidase-mimicking catalytic behavior to induce chromogenic reactions, thus enabling one to start or stop the catalytic progress easily via applying or withdrawing light irradiation. Meanwhile, the quantum dot material can exhibit bright photoluminescence, which provides the fluorometric channel to sense targets. When Hg2+ is introduced, it rapidly leans toward Mn–CdTe through electrostatic interaction and Te–Hg bonding and induces the aggregation of the latter. As a result, the luminescence of Mn–CdTe is dynamically quenched, and the masking of active sites in aggregated Mn–CdTe leads to the decrease of light-initiated oxidase-mimetic activity. According to this principle, a new fluorometric/colorimetric bimodal method was established for Hg2+ determination with excellent performance. A 3D-printed portable platform combining paper-based test strips and an App-equipped smartphone was further fabricated, making it possible to achieve in-field sensing of the analyte in various matrices.

The mathematical model of quantum dots pair orientation under laser radiation field

One approach for the formation of structures with complex geometries at the nanoscale is the step-by-step assembly. In this case, it is necessary to be able to estimate the time required to establish orientational equilibrium for a preformed pair of particles. This process is statistical in nature and depends on the mechanism of interaction of the ensemble with the external field. The orientation of particles in an alternating field is associated with certain relaxation times, which depend on the viscosity and temperature of the medium, as well as on the geometric structure of the samples. This paper proposes an mathematical model of the process of establishing the distribution of nanoparticles pairs orientations taking into account the friction force, thermal motion, and the orienting laser field. A statistical orientation distribution was obtained for CdTe particles in the field of moderate laser radiation, and the average time for establishing orientational equilibrium was estimated.

A facile hydrothermal synthesis of novel CeO2/CdSe and CeO2/CdTe Nanocomposites: Spectroscopic investigations for economically feasible photocatalytic degradation of Congo red dye

The photocatalytic activity of CeO2 nanoparticles in the visible spectrum can be greatly improved via incorporating of narrow band gap semiconductors like CdSe and CdTe into CeO2 structure bringing out a new heterojunction structure to boost the visible-light absorption efficiency. Therefore, CeO2/CdSe and CeO2/CdTe nanocomposites were felicitously fabricated through a simple and effective hydrothermal route without using any expensive surfactant or capping agent keeping a molar ratio of 1:1:1 (Ce:Cd:Se/Te). The as-synthesized materials were identified utilizing different spectroscopic investigation techniques such as X-ray diffraction (XRD), Raman spectroscopy and Solid-state UV-diffuse reflectance spectroscopy (UV-DRS). Transmission electron microscopy (TEM) confirmed the semi-spherical structure of all as-synthesized samples with deposition of CdSe and CdTe particles on CeO2 surface leading to binary composites formation. The specific surface areas (BET) were explored to be 55.2 m2/g and 20.8 m2/g for CeO2/CdSe and CeO2/CdTe nanocomposites, respectively. The photocatalytic performance of CeO2/CdSe and CeO2/CdTe nanocomposites was tested under visible-light irradiation on an aqueous solution of Congo red (CR) dye using an energy-saving lamp (LED). The degree of degradation was monitored by UV–Vis spectroscopy and verified by chemical oxygen demand (COD) studies. The photocatalytic degradation efficiency of CeO2/CdSe nanocomposite (97.3%) was about 3.5 times greater than of bare-CeO2 NPs (28.2%) within only 150 min of irradiation. Photo-induced electrons were found to be the primary active participating species that was verified using the relevant radical scavengers and a clear photocatalytic mechanism was proposed. The recycling test confirmed that CeO2/CdSe is a highly photostable catalyst with four-repeating cycles displaying degradation efficiencies, respectively, at 97.3%, 96.1%, 95.5% and 95.1%. The structural stability of the operated catalyst was confirmed by XRD studies.

Size- and Surface-Dependent Solubility of Cadmium Telluride in Aqueous Solutions

Due to the toxicity of cadmium (Cd) and the scarcity of telluride (Te), CdTe-based photovoltaic modules have been under discussion during the last few years. In particular, the stability of CdTe in aqueous solutions is under debate. Here we show that the stability of CdTe depends not only on the pH of water-based solutions but also on size and surface treatment of CdTe particles. We compare milled module pieces with CdTe powders of different particle size. The leaching of CdTe is conditioned by the outdiffusion of Cd and Te at the interface between CdTe particles and the aqueous solution. The smaller the particle size, the faster the leaching. Therefore, milled module pieces decompose faster than CdTe powders with relatively large grains. We observe a dependence on time t according to t0.43. The room temperature diffusion coefficients are calculated as DCd ≈ 3 × 10−17 cm2/s for Cd, and DTe ≈ 1.5 × 10−17 cm2/s for Te in pH4. The chemical instability in aqueous solutions follows thermodynamic considerations. The solution behavior of Cd and Te depends on the pH value and the redox potential of the aqueous solutions. Chemical treatments such as those used in solar cell production modify the surface of the CdTe particles and their leaching behavior.

Chalcogenide thin film multilayer structure for solar cell applications

Nanocrystalline semiconductor thin films of TiO2, CdS and CdTe were prepared by various techniques. TiO2 thin films of controlled thickness and optimized electrical properties were prepared by Langmuir Blodgette (LB) technique. CdTe nanoparticles were prepared by hydrothermal technique whereas CdS nanoparticles were prepared by solvothermal technique. Structural, optical and electrical characterizations of TiO2 thin films, CdS and CdTe nanoparticles were carried out. UV–Visible absorption studies indicated that particle size of CdTe was varying with refluxing time. X-ray diffraction studies indicated the CdS particle of size about 2.4 nm with single phase cubic structure and CdTe particles of size 3 nm with crystal phase zinc blende structure. Photosensitivity studies were carried out on Si/TiO2/CdS/CdTe multilayer structure using two different electrolytes (Na2SO4 and mixture of Na2S:Na2SO3) in photoelectrochemical cell (PEC) configuration. Two electrolytes were used to study the PEC effect on photovoltaic properties. The study showed higher photocurrent with Na2S:Na2SO3 electrolyte.

In silico study of the atomic and electronic structure of quantum dots of the CdTe family doped with atoms of rare earth elements

An in silico study of semiconductor quantum dots of the CdTe family doped with atoms of rare earth elements is performed based of density functional theory. An ab initio computer design of quantum dots based on CdTe nanoparticles doped with Eu и Gd atoms is carried out. Partial densities of states of CdTe:Eu and CdTe:Gd quantum dots are calculated and analyzed. X-ray absorption near edge (XANES) spectra near the Eu K-, L 1-, and L 3- and Gd K-, L 1-, and L 3-edges of CdTe:Eu and CdTe:Gd quantum dots are calculated. The sensitivity of XANES spectroscopy for the verification of parameters of a nanosized atomic structure of quantum dots based on CdTe particles doped with atoms of rare earth elements and the determination of the local atomic structure around the atoms of rare earth elements in quantum dots is demonstrated.

Thermal and photo stability of glutathione-capped cadmium telluride quantum dots.

Nanoparticles (NPs) are increasingly being used in a number of applications that include biomedicine, biological labeling and cancer marker targeting, and their successful storage is important to preserve their viability. A systematic investigation of the thermal and photo stability of chemically stabilized cadmium telluride (CdTe) quantum dots (QDs) under various storage conditions either in solution or as dried nanoparticles has not been published. Here we report experiments involving chemically synthesized glutathione-capped CdTe QDs whose photoluminescence spectra were examined initially and then periodically during storage times up to 76 days. Samples of dried QDs or QDs in solution (water or buffered) were examined under different light conditions including complete darkness, constant 12,000 lux incident light, and under diurnal sunlight; at temperatures ranging from -80 °C to room temperature. Though QDs stored in solution in the dark at -80 °C lost only 50% of peak fluorescence (FL510) within 2 weeks, solution-stored QDs exposed to sunlight at room temperature showed FL510 drops of 85% in the first 24 hours. In contrast, QDs precipitated from aqueous solution, dried and stored in time course experiments in the presence of atmospheric oxygen--when resuspended in water--lost an average of only 12% FL510 over 76 days under all conditions tested, even in direct sunlight. Glutathione-capped CdTe particles can be stored as dried nanoparticles for extended periods of time, enhancing their viability in biomedicine, biological labeling and cancer marker targeting.

Facile synthesis and transformation of Te nanorods to CdTe nanoparticles

Luminescent cadmium telluride nanoparticles were synthesized from the reaction intermediate tellurium nanorods as tellurium source at 100°C through colloidal approach. Oxyanion source of tellurium, (i.e.) potassium tellurite (K2TeO3) was used as precursor to synthesize the tellurium nanorods under the low temperature process without any surfactant in various volumes of water. Thioglycolic acid (TGA) was employed as capping agent for the synthesis of CdTe nanoparticles. Absorption and emission spectra of the prepared nanoparticles clearly indicate the size dependent nature of the particles. SEM and EDX analyses of the nanorods reveal the shape of the synthesized nanorods and the presence of elemental tellurium without any impurities. XRD analysis of the prepared samples confirms the existence of trigonal phase of tellurium nanorods (t-Te) and the formation of CdTe particles with cubic zincblende structure. The size distribution of the prepared CdTe nanoparticles was analyzed through TEM analysis. It was found that considerable influence of solvent on morphology of the synthesized tellurium nanorods. The synthesis mechanism of one dimensional structure as seeds for zero dimensional nanoparticles was analyzed.

Preparation and Physicochemical Properties of Supramolecular Hemoprotein Assembly Via Heme-Heme Pocket Interaction

Protoheme IX is the simplest and most well-known iron porphyrin in nature and acts as a cofactor in many hemoproteins such as hemoglobin, myoglobin, cytochrome P450, and horseradish peroxidase. The cofactor, heme b, is bound in the heme pocket via coordination and multiple noncovalent interactions. Therefore, heme b is released from the heme pocket upon acidic condition to yield the apoprotein. The apoprotein is capable of binding heme b again at neutral pH value and then the reconstituted protein is available. To functionalize a hemoprotein, it will be very effective for replacing native heme with an appropriate heme analog. Our group has recently focused on the following three methods to prepare an artificial prosthetic group.1) (i) Introduction of functional groups at the terminal of the heme-propionate side chains. (ii) Modification of the framework of the prosthetic group. (iii) Replacement of a metal substitution in the core of the porphyrin framework. In our previous work, we prepared several types of supramoelcular hemoprotein assembies via interprotein heme–heme pocket interaction by method (i) vide supra.2) We first prepared a heme moiety with a maleimide group at the terminal of one of the heme-propionate side chains. The heme moiety was then introduced to a cysteine residue positioned on the surface of an apocytochrome b 562 mutant (H63C) via a covalent linkage. The heme moiety-linked apoprotein provided a linear hemoprotein assembly determined by an AFM technique.3) The AFM image clearly demonstrates the 1D protein fiber including more than 100 proteins on a graphite substrate. Next, we tried to immobilize the hemoprotein polymers onto a gold surface, gold electrode or gold nanoparticle. Particularly, the heme-attached gold surface provided the hemoprotein assemblies with the number of 6–8 protein layers on the electrode upon the addition of the heme-linked apoproteins.4) The assembly structure on the electrode was mainly analyzed by the AFM technique and QCM measurement. Furthermore, the immobilization of zinc cytochrome b 562 polymer on a gold electrode gave efficient photocurrent generation in the presence of methyl viologen as an electron mediator. In addition, it is found that heme-immobilized gold nanoparticles provide a unique self-assembly upon the addition of apohemoprotein dimer.5) The supramolecular porphyrin array mediated by hemoprotein matrix serves as a new way to create bionanomaterials. For example, we have prepared a myoglobin–quantum dot conjugate by a heme-immobilized CdTe particle.6) In this presentation, we report the construction of several supramolecular hemoprotein assemblies in a solution and on a metal surface. 1) T. Hayashi, In Handbook of Porphyrin Science; K. M. Kadish, K. M. Smith, R. Guilard, Eds.; World Scientific publishing: Singapore, 2010; Vol. 5, pp 1–69.2) K. Oohora, A. Onoda, T. Hayashi, Chem. Commun., 48, 11714–11726 (2012) (Feature Article). 3) H. Kitagishi, K. Oohora, H. Yamaguchi, H. Sato, T. Matsuo, A. Harada, T. Hayashi, J. Am. Chem. Soc., 129, 10326–10327 (2007). 4) A. Onoda, Y. Kakikura, T. Uematsu, S. Kuwabata, T. Hayashi, Angew. Chem. Int. Ed., 51, 2628–2631 (2012). 5) A. Onoda, Y. Ueya, T. Sakamoto, T. Uematsu, T. Hayashi, Chem. Commun., 46, 9107–9109 (2010).6) A. Onoda, T. Himiyama, K. Ohkubo, S. Fukuzumi, T. Hayashi, Chem. Commun., 48, 8054–8056 (2012).

Synthesis of Cadmium and Lead Telluride Nanoparticles: Examples of Oriented attachment Growth Mechanism

ABSTRACTThe synthesis of hexadecylamine capped (HDA) CdTe and PbTe via a simple hybrid solution based high temperature route is described. In this method the tellurium is first reduced to form the telluride salt followed by reaction with the metal salt and finally thermolysis in a coordinating solvent. The metal salt and reaction temperature played an important role in the morphology and growth mechanism of the particles. The CdTe particles where in the form of rods and spheres whereas the PbTe nanoparticles were in the form of nanowires. The oriented attachment mechanism is proposed for the growth of elongated particles under certain reaction conditions.

Effect of solvent nature on the stability of highly dispersed and nanosized cadmium telluride

Processes of adsorption modification of particle surface of disperse phase upon introduction of thioglycolic acid into highly dispersed systems based on CdTe were studied. It was shown that the selection of stabilizer composition and solvent enables purposeful effect on the properties of these systems. The stabilization of CdTe particles in highly dispersed and nanosized systems was found to be best conducted with the use of methanol and ethanol as a solvent. The postsynthetic treatment of colloidal solutions of CdTe nanocrystals with absolute ethyl alcohol was found to improve considerably their photoluminescent properties.

Vplyv nanochastynok CdTe na utvorennya J-ahrehativ tiamonometyntsianinovykh barvnykiv

Conditions of J-aggregate formation have been studied for three types of thiamonomethinecyanine dyes, the structures of which differ from one another by their end groups, and the dependences of those conditions on the dye concentration and the type of dye interaction with CdTe nanoparticles with a diameter of 3 nm in aqueous dispersions have been analyzed. The dye structure is found to influence the efficiency of the J-aggregate formation in solutions and films. It is also found that CdTe quantum dots (QDs) stabilized by thioglycolic acid can adsorb J-aggregates of dye molecules on their surface. It is shown for the first time that the hybrid structure dye–CdTe can emerge owing to the interaction between the negatively charged dye molecules and the negatively charged surface of QDs forming neutral aggregates. No process of energy transfer from the dye to a CdTe particle was detected in the dimer–CdTe and J-aggregate–CdTe systems.

Growth and defect studies of CdTe particles

The paper reports the epitaxial growth of cadmium telluride (CdTe) particles by thermal deposition on cleaved planes of (001)NaCl and (001)KBr. Using high resolution transmission electron microscopy and electron diffraction it was shown that CdTe particles could have different orientation and phase (cubic or hexagonal) depending on the substrate temperature. Their most common defects are twins and stacking faults.

A Comparative Study of CdTe Quantum Dots and CdTe@SiO2 Nanoparticles: Fabrication and Cytotoxicity in HEK293 Cells

Quantum Dots have shown remarkable potentials in biomedical research. Herein, we reported the effects of CdTe quantum dots (QDs) and CdTe@SiO2 nanoparticles (NPs) on human embryonic kidney 293 (HEK 293A) cells with the aim of investigating their in vitro cytotoxicity. The CdTe@SiO2 particles were prepared by reverse microemulsion method. The structural morphology of the CdTe and hydrophilic silica-coated CdTe particles were characterized by transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) spectrometry and photoluminescence (PL) spectrometry. The in vitro cytotoxicity of CdTe QDs and CdTe@SiO2 nanoparticles was assessed in 293A cells using standard MTT assay, western blot and fluorescent microscopy. The results showed that the CdTe and CdTe@SiO2 particles were relatively uniform with the diameter of about 3.8 nm, 75 nm respectively. The cell viability and the adhesion ability were similar to the control 293A cells. The level of the fibronectin protein expression was decreased with the increasing concentration of CdTe while the no effects were observed on expression of beta-actin in CdTe as well as CdTe@SiO2 treated cells even at highest concentration of 45 microg/mL which demonstrated their good biocompatibility to 293A cells. The results indicate that the CdTe@SiO2 nanoparticles are attractive candidates for biological imaging studies as expected.

Phase assembly and photo-induced current in CdTe-ZnO nanocomposite thin films

Sequential radio-frequency sputtering was used to produce CdTe-ZnO nanocomposite thin films with varied semiconductor-phase extended structures. Control of the spatial distribution of CdTe nanoparticles within the ZnO embedding phase was used to influence the semiconductor phase connectivity, contributing to both changes in quantum confinement induced spectral absorption and carrier transport characteristics of the resulting nanocomposite. An increased number density of CdTe particles deposited along the applied field direction produced an enhancement in the photo-induced current observed. These results highlight the opportunity to employ long-range phase assembly as a means to control optoelectronic properties of significant interest for photovoltaic applications.

Facile Synthesis of Organically Capped CdTe Nanoparticles

A simple method for the preparation of tri-n-octylphosphine oxide (TOPO) and hexadecylamine (HDA) capped CdTe particles have been employed in this study. The method involves the reduction of tellurium in water followed by the addition of the cadmium salt and thermolysis in TOPO and HDA. The influence of the reduction time (2, 4 and 6 h) of tellurium on the optical properties was investigated. The particles were characterised by electron microscopy and X-ray diffraction techniques.

Syntheses of CdTe Quantum Dots and Nanoparticles through Simple Sonochemical Method under Multibubble Sonoluminescence Conditions

Colloidal cadmium telluride (CdTe) quantum dots (QDs) and their nanoparticles have been synthesized by one pot sonochemical reactions under multibubble sonoluminescence (MBSL) conditions, which are quite mild and facile compared to other typical high temperature solution-based methods. For a typical reaction, and tellurium powder with hexadecylamine and trioctylphosphine/trioctylphosphineoxide (TOP/TOPO) as a dispersant were sonicated in toluene solvent at 20 KHz and a power of 220W for 5-40 min at 60 . The sizes of CdTe particles, in a very wide size range from 2 nm-30 , were controllable by varying the sonicating and thermal heating conditions. The prepared CdTe QDs show different colors from pale yellow to dark brown and corresponding photoluminescence properties due mainly to the quantum confinement effect. The CdTe nanoparticles of about 20 nm in average were found to have band gap of 1.53 eV, which is the most optimally matched band gap to solar spectrum.

Solution-Processed Sintered Nanocrystal Solar Cells via Layer-by-Layer Assembly

Solar cells made by high temperature and vacuum processes from inorganic semiconductors are at a perceived cost disadvantage when compared with solution-processed systems such as organic and dye-sensitized solar cells. We demonstrate that totally solution processable solar cells can be fabricated from inorganic nanocrystal inks in air at temperature as low as 300 °C. Focusing on a CdTe/ZnO thin-film system, we report solar cells that achieve power conversion efficiencies of 6.9% with greater than 90% internal quantum efficiency. In our approach, nanocrystals are deposited from solution in a layer-by-layer process. Chemical and thermal treatments between layers induce large scale grain formation, turning the 4 nm CdTe particles into pinhole-free films with an optimized average crystallite size of ∼70 nm. Through capacitance-voltage measurements we demonstrate that the CdTe layer is fully depleted which enables the charge carrier collection to be maximized.

Surface-plasmon-enhanced photocurrent generation of CdTe nanoparticle/titania nanosheet composite layers on Au particulate films

Multilayer films composed of Au particle/titania nanosheet (TNS)/CdTe nanoparticle were successfully prepared using a layer-by-layer-deposition technique. CdTe nanoparticles were accumulated as the topmost layer on TNS/poly(diallyldimethylammonium) (PDDA) bilayers deposited on the substrates of an Au particle film or an F-doped SnO 2 (FTO) electrode. CdTe nanoparticles were acted as a photosensitizer. The photogenerated electrons in CdTe nanoparticles were injected into the conduction band of titania nanosheets to produce anodic photocurrent at a more positive potential than −0.4 V vs. Ag/AgCl. The magnitude of photocurrent was much larger for the films prepared on the Au particle film rather than that on the FTO electrode. Furthermore, with an increase in the thickness of (TNS/PDDA) bilayers, that is, the distance between Au and CdTe nanoparticles, the photocurrent was drastically decreased. The enhancement factor of photocurrent, defined as the ratio of the magnitude of photocurrent obtained with CdTe particle layer immobilized on Au layer to that on FTO, was varied from 2 to 10 by changing the wavelength of irradiation light. The broad peak at 520 nm appeared in the action spectrum of the enhancement factor and its profile roughly corresponded to the localized surface plasmon resonance peak of Au particle layer whose peak wavelength was ca. 540 nm. These facts indicated that the photoexcitation of the surface plasmon of Au particles, which produced a locally enhanced electric field near Au particle layer, played an important role in the increase in the photoexcitation probability of CdTe nanoparticles deposited as the topmost layer.

A facile route to shape controlled CdTe nanoparticles

Hexadecylamine (HDA) capped CdTe nanoparticles have been synthesized using a facile hybrid solution based/thermolysis route. This method involves the reaction by the addition of an aqueous suspension or solution of a cadmium salt (chloride, acetate, nitrate or carbonate) to a freshly prepared NaHTe solution. The isolated CdTe was then dispersed in tri-octylphosphine (TOP) and injected into pre-heated HDA at temperatures of 190, 230 and 270 °C for 2 h. The particle growth and size distribution of the CdTe particles synthesized using cadmium chloride as the cadmium source were monitored using absorption and photoluminescence spectroscopy. The final morphology of the CdTe nanoparticles synthesized from the various cadmium sources was studied by transmission electron microscopy (TEM) and high resolution TEM. The cadmium source has an influence on the final morphology of the particles.